Combine the soy sauce, vinegar, sesame oil, and 1 Tbs. of the peanut oil in a small bowl; set aside. Turn on the exhaust fan and heat a heavy 12-inch skillet or large wok over high heat for 2 minutes. When the pan is hot, pour in the remaining 2 Tbs. peanut oil; a couple of seconds later, add the black beans (if using), the chile flakes, broccoli, red pepper, garlic, and ginger. Season the mixture well with salt and cook, tossing or stirring often, until the broccoli deepens to a dark green and browns in places, 3 to 4 minutes. Reduce the heat to medium low, carefully add the water (it will steam), and cover the pan with the lid ajar. Cook until the broccoli softens but still has some crunch, about 4 minutes. (If the water evaporates before the broccoli is done, add more, 1 Tbs. at a time.) Stir the soy sauce mixture well and drizzle it over the broccoli, toss well, and serve immediately.